TODOs:

- [x] Add assertions to the test to ensure that the git status is
propagated
- [x] Get collaboration working
- [x] Test opening a git repository inside another git repository
- [x] Test opening the sub-folder of a repository that itself contains
another git repository in a subfolder

Fixes:
- Fixes https://github.com/zed-industries/zed/issues/10154
- Fixes https://github.com/zed-industries/zed/issues/8418
- Fixes https://github.com/zed-industries/zed/issues/8275
- Fixes https://github.com/zed-industries/zed/issues/7816
- Fixes https://github.com/zed-industries/zed/issues/6762
- Fixes https://github.com/zed-industries/zed/issues/4419
- Fixes https://github.com/zed-industries/zed/issues/4672
- Fixes https://github.com/zed-industries/zed/issues/5161

Release Notes:

- Added support for opening subfolders of git repositories and treating
them as part of a repository (show git status in project panel, show git
diff in gutter, git blame works, ...)
([#4672](https://github.com/zed-industries/zed/issues/4672)).

Demo video:


https://github.com/zed-industries/zed/assets/1185253/afc1cdc3-372c-404e-99ea-15708589251c